Process for electroplating an aluminum wire

ABSTRACT

Aluminum wire, of either pure aluminum or an aluminum alloy, is plated with a firm layer of at least one of nickel, copper, tin, zinc, or cadmum by treating the wire with an aqueous solution of hydrofluoric and hydrochloric acids and then electroplating the wire with the metal. The electrolyte is a solution of a fluoroborate or sulfamate salt of the metal. The aluminum wire so plated possesses superior conductivity and may be readily soldered.

United States Patent Hansson Feb. 18, 1975 [5 PROCESS FOR ELECTROPLATING AN 3,099,609 7/1963 Katayose 204/33 MIN W ALU UM IRE FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Hans Hansson, Souemlmai 1,139,713 11/1962 Germany 204/33 Sweden [73] Assignee: Telefonaktiebolaget L M Ericsson, primary E i j h R Mack Stockholm Sweden. Assistant ExaminerW. 1. Solomon [22] Filed; 7 1973 Attorney, Agent, or Firm-Hane, Baxley & Spiecens [2]] Appl. No: 336,171

Related US. Application Data [57] ABSTRACT [63] Continuation of Ser. No. 128,742, March 29, 1971, Aluminum Wife, of either P aluminum or an alumiabandoned. num alloy, 15 plated with a firm layer of at least one of nickel, copper, tin, zinc, or cadmum by treating the [52] US. Cl 204/28, 204/33, 204/49, wire with an aqueous solution of hydrofluoric and hy- 204/50 R, 204/52 R, 204/54 R, 204/55 R drochloric acids and then electroplating the wire with [51] Int. Cl C23b 5/58 he metal. The electrolyte is a solution of a fluorobo- [58] Field of Search 204/33, 28 rate or sulfamate salt of the metal. The aluminum wire so plated possesses superior conductivity and may be [56] References Cited readily soldered.

UNITED STATES PATENTS 3 Claims, 2 Drawing Figures 3,003,933 10/1961 Atkinson 204/33 Pmmgmzmams ,3, 867 2 .1

FIG. 2

PROCESS FOR ELECTROPLATING'AN ALUMINUM WIRE This is a continuation of application Ser. No. 128,742, filed Mar. 29, 1971, and now abandoned.

SPECIFICATION This invention relates to electrical conductors such as wires or cables. It particularly relates to improved wires or cables of aluminum or alloys of aluminum and to processes for the manufacture of such wires and cables.

BACKGROUND ductivity. Another serious disadvantage of aluminum and alloys thereof is the difficulty to make good contacts with themselves or other metals. For example, an aluminum wire cannot be readily soldered to another aluminum wire or to another metal. This makes it difficult and very dangerous to use aluminum wires or cables, for instance, in house wiring. When the term *aluminum is used hereinafter, it shall refer to both the aluminum metal and alloys of aluminum.

To obtain aluminum wire free of the afore-indicated disadvantages, aluminum wire has been coated with other metals such as copper to obtain aluminum-metal bonds. These coated wires have better conductivity and make better contacts. Such coatings can be obtained by heat-treatment of the aluminum with the metal copper as described in Texas Instruments Bulletin No. 516-TB, -768 or through electrochemical deposition of the metal on the aluminum. However, the bonds between the coating and the aluminum were not strong and on use the coating frequently rubbed off or peeled off. Furthermore, the process was not readily controllable to provide a coating of both uniform and desired thickness. Usually, the coatings were thicker than desired, thereby increasing the costs and reducing the ductility of the coated wires. Desirably, the thickness of the coating should be about 1.0 to 1.5 microns.

TH E INV ENTION It is accordingly an object of the present invention to provide a wire of aluminum which is coated with an inexpensive metal.

It is another object of the present invention to provide a coating of a metal on an aluminum wire which coating is strongly bound to the aluminum and does not rub off or peel off during use, particularly on abrasion crons.

It is a further object of this invention to provide a process for preparing an aluminum wire coated with a metal, said coated wire having the desirable properties described above.

In accordance with my invention, I provide a process for coating an aluminum wire with a metal which comprises the steps:

l. treating the wire with an aqueous solution of hydrofluoric and hydrochloric acid, and

2. electroplating the wire with a metal wherein the electrolyte is a salt of the metal, the anode is the metal, and the cathode is the aluminum wire.

In practicing the invention the aluminum wire may be of substantially pure aluminum metal or a suitable alloy thereof such as, for example:

aluminum 98.5-99.8 percent, iron 0.2 1.5 percent aluminum 99.1 percent, iron 0.15 percent, magnesium 0.15 percent aluminum 99.46 percent, copper 0.40 percent, magnesium 0.14 percent.

The aluminum wire is preferably cleaned prior to the acid treatment by removing any metallic or other particles adhering thereto and then by dissolving any greases or lubricants on the wire in a suitable solvent, such as ethylene dichloride or carbon tetrachloride. The solvent is preferably volatile so little time will elapse between the solvent treatment and the following acid treatment.

The acid treatment is carried out by passing the wire through an aqueous solution containing hydrofluoric and hydrochloric acids. The solution desirably contains from about 3 to 5 percent parts by weight of concentrated hydrofluoric acid (48 percent) and from about 29 to 30 percent parts of concentrated hydrochloric acid (37.9 percent) and sufficient water to make up to parts by weight. Preferably, a solution containing 4 parts by weigt 48 percent hydrofluoric acid, 30 parts by weight 37.9 percent hydrochloric acid and 66 parts by weight water is used. The acid treatment may be carried out at a temperature from about 55 to 65C, but

is preferably carried out at about 60C. This treatment serves to etch the aluminum wire and aids in providing a better contact between the aluminum and the coating.

After treatment with the acid the wire is passed through hot water to remove any adhering acid.

The aluminum wire is then passed through an aqueous electrolyte containing one or more salts of the metal or metals that is to be plated on the aluminum wire between anodes of the metal. While numerous salts can serve as electrolytes, I prefer to use the fluoroborate or sulfamate salts in concentrations of about 200 to 250 g. per liter. In addition, I may add to the electrolyte about I g. per liter each of the free acid and of the metal. The pH of the electrolyte solution is about 2 and may be varied between a range of about 2 to 2.5.

Metals which have been used for coating the aluminum wire include nickel, copper, tin, zinc and cadmium.

The electroplating may be carried out at a temperature of about 20 to 60C, but is preferably carried out at about 40C.

The current density and voltage can be varied to suit the conditions under which the process is practiced. I have found that a current density of about 20 amps/dm and a voltage of about 6 volt are satisfactory.

DETAILED DESCRIPTION OF AN APPARATUS, FOR CARRYING OUT THE METHOD OF THE INVENTION The method of carrying out the process of the present invention is illustrated in the drawings and the Example which follows:

FIG. 1 represents a flow scheme of the process; and

FIG. 2 is a sectional view of the unit along the line 2-2 of FIG. 1.

In the figures, represents the unit for carrying out the coating operation.

The wire 9 is first degreased in a trichloroethylene degreasing unit 11 and then passes repeatedly as shown in FIG. 2 over two blocks of driven rollers 12 through an acid bath 13 which contains a mixture of hydrofluoric acid, hydrochloric acid and water. This use of the acid bath produces the necessary perfect bond between the wire and the nickel plating when composed as hereinafter stated and kept carefully balanced. The wire is- 'wiped off and washed in running hot water 19 before passing two rollers 14 and then enters the plating bath 16 and passes it many times over two blocks of driven rollers 15, of which at least one is connected to the negative pole of a DC. source each time between pairs of metal anodes such as nickel anodes 17 which anodes are connected to the positive pole of the DC source. The wire is again wiped off and washed in running hot water 20. Finally, it is reeled over driven rollers 18.

The plating bath may be based on either one of two well known fluoborate or sulfamate processes, and it must be balanced in its composition in order to produce an extremely fine-grained structure and to enable the plating to penetrate all small pittings as may have been caused in the acid bath. Careful control and adjustment of bath temperatures and bath compositions are necessary for the production of a quality product. The fact that the fluoborate and sulfamate processes enable extremely high current densities to be kept in the plating bath and the fact that all systems of rollers are driven allow the process to be run at high speed and low costs.

The example below shows the operating conditions and dimensions of the units for the plating of an aluminum wire with nickel. This example is given only by way of illustration and is not to be considered as limit- Length of the acid baths in mm 4300 Length of the plating baths in mm 4300 Length of the hot water washing baths in mm 4300 Length of the wire path in the acid bath in m ca 80 Length of the wire path in the plating bath in m ca 80 Length of the wire path in the hot water washing in m 4.3 Wire speed in m/sec ca 6 Acid bath formula:

Hydrofluoric acid, 48%

by weight 4 Hydrochloric acid, 37.971

by weight 30 Water dist., /r by weight 66 Plating bath formula:

Nickelfluoborate, g/l 683 Nickel. g/l 172 Free boric acid, g/l 33 Acid bath working conditions:

Temperature, "C 60 Plating bath working conditions:

Temperature. C 40 pH. colorimetric 2.0 Current density. Amp/dm ca 20 Bath voltage. V ca 6 Ur'ii? '5aaiiioas"&smbaa, an alumin um wire 2.5 mm in cross-sectional area will be plated with a nickel coating having a thickness of 1.5 microns.

By means of the above-described process, the nickel coating is built up as a layer of connected islands completely covering and penetrating the aluminum surface so that all small porosities are filled with nickel. Thus a very strong bond is established between the aluminum surface and the nickel coating. 'rse'"metaeaafaaiummuawire prepared by the process described has the same excellent contact properties as a copper wire and may be tin soldered in the same way as a copper wire. It may be drawn down to smaller dimensions without losing its contact properties. Even subsequent hot tinning may be carried out with excellent results and the hot tinned wire has the same smooth and bright surface as a hot tinned copper wire.

Similar results were obtained when a sulfamate salt was used in place of a fluoroborate and a metal such as copper, tin, zinc or cadmium was used in coating. If desired, mixtures of two or more of the metals may be used.

What is claimed is:

I. In a process for electroplating an aluminum wire with a metal selected from the group consisting of nickel, copper, tin, zinc and cadmium which comprises the steps:

. i. etching the wire through an acid bath,

ii. rinsing the wire by passing it through water, and

iii. electroplating the wire with at least one of said metals by passing the wire through an electrolyte which contains at least one ofa fluoroborate or sulfamate salt of at least one of said metals, the aluminum wire being the cathode and the selected metal the anode,

said acid bath consisting of4 percent by weight of 48 percent hydrofluoric acid, 30 percent by weight of 37.9 percent of hydrochloric acid, and 66 percent by weight of water, and being at a temperature of about C, said wire being in contact with the acid bath for about 13 seconds.

2. The ir'bskib'rdin to claim 1 wherein the aluminum wire is composed of substantially pure aluminum.

3. The process according to claim 1 wherein the aluminum wire is composed of an aluminum alloy selected from the group of alloys having the following compositions:

aluminum 98.5-99.8 percent and iron 1.5-0.2 percent,

aluminum 99.1 percent, iron 0.75 percent, and magnesium 0.15 percent and aluminum 99.45 percent, copper 0.40 percent, and 

1. IN A PROCESS FOR ELECTROPLATING AN ALUMINUM WIRE WITH A METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL, COPPER, TIN, ZINC AND CADMIUM WHICH COMPRISES THE STEPS: I. ETCHING THE WIRE THROUGH AN ACID BATH, II. RINSING THE WIRE BY PASSING IT THROUGH WATER, AND III. ELECTROPLATING THE WIRE WITH AT LEAST ONE OF SAID METALS BY PASSING THE WIRE THROUGH AN ELECTROLYTE WHICH CONTAINS AT LEAST ONE OF A FLUOROBORATE OR SULFAMATE SALT OF AT LEAST ONE OF SAID METALS THE ALUMINUM WIRE BEING THE CATHODE AND THE SELECTED METAL THE ANODE, SAID ACID BATH CONSISTING OF 4 PERCENT BY WEIGHT OF 48 PERCENT HYDROFLUORIC ACID, 30 PERCENT BY WEIGHT OF 37.9 PERCENT OF HYDROCHLORIC ACID, AND 66 PERCENT BY WEIGHT OF WATER, AND BEING AT A TEMPERATURE OF ABOUT 60*C, SAID WIRE BEING IN CONTACT WITH THE ACID BATH FOR ABOUT 13 SECONDS.
 2. The process according to claim 1 wherein the aluminum wire is composed of substantially pure aluminum.
 3. The process according to claim 1 wherein the aluminum wire is composed of an aluminum alloy selected from the group of alloys having the following compositions: aluminum 98.5-99.8 percent and iron 1.5-0.2 percent, aluminum 99.1 percent, iron 0.75 percent, and magnesium 0.15 percent and aluminum 99.45 percent, copper 0.40 percent, and magnesium 0.15 percent. 